My aforesaid application Ser. No. 130,615 discloses a method of and apparatus for the recovery of waste energy which includes a heat exchanger which receives heated waste water discharged from a dishwasher or the like to preheat the cold water supply to a hot water heater which supplies the dishwasher with hot water for the wash and rinse cycles. Such application also discloses the desirability of controlling the flow of waste water to the heat exchanger at a time when the dishwasher or the like requires hot water from the hot water heater, so that preheated feed water will be supplied. This heat exchanger is mounted in the upper portion of a unit having a housing, while a lower portion of the unit contains a tank for receiving the waste dishwater which passes through a removable screen above the tank. The tank is bordered by an overflow partition which separates an outlet area therefrom. The collected waste water is pumped from a sump beneath the tank to one inlet of the heat exchanger above, while the used waste water, after heat exchange, is discharged into the outlet area. The unit is installed beneath the dish counter of the dishwasher, or a similar closely adjacent position, rather than at a remote location adjacent to the hot water heater, as in my prior application Ser. No. 920,660. Since a hot water heater is often located at some distance from the dishwasher, under which the unit is placed, and the hot water heater may supply other facilities, such as wash rooms, sinks and the like, insulation is usually necessary in order to prevent the preheated feed water from becoming unduly cooled by passage to the hot water heater. However, the expense of installing the piping and insulation may reduce the savings due to recovery of waste energy.
There are two general types of dishwashers in use, one being referred to as a "high temperature" dishwasher and operates with water at about 180.degree. F. for rinsing and the waste water at about 140.degree. F. Normally, the wash water is used rinse water which has been retained in a separate space in the dishwasher for that purpose and then saponified, so that hot water is drawn from the hot water heater during the rinse cycle only. Thus, the used wash water would be saved until the next rinse cycle, while the hot water heater would be capable of heating the water to 190.degree. or 195.degree. F. to supply rinse water at 180.degree. F. The other is referred to as a "low temperature" type and utilizes a special detergent. This type operates with water at a temperature of about 140.degree. F. for rinsing, with the waste water at about 125.degree. F. In each type, the amount of water used for rinsing is within the capacity of electric heaters to produce.
Among the objects of this invention are to provide a novel method and unit for recovering waste energy, particularly from equipment such as a dishwasher; to provide a method and unit which involves a heat exchanger for preheating incoming water to be heated to an appropriate temperature for rinsing dishes through heat exchange with the waste water from the dishwasher, normally wash water; to provide such a unit which may be positioned adjacent or beneath a dishwasher and also supply hot water thereto, without the necessity for transferring the waste water or the hot water being supplied through pipes for any great distance; to provide such a unit in which special provision is made for avoiding overheating the electric heaters and thereby burning out the same, when hot water for rinsing is supplied to a high temperature dishwasher, but which special equipment may be omitted when hot water is supplied to a low temperature dishwasher; and to provide such a method and unit which are effective and efficient in use.